The present invention relates generally to a film for use in packaging applications and, more particularly, to such a film that has condensation control characteristics.
The most common way to wrap pallets is the use of a film, such as a stretch film, which is wrapped around a pallet to provide stability to a pallet load and some degree of product protection. To increase protection, a top sheet or a loose plastic bag is sometimes added to the pallet prior to being wrapped by the stretch film. However, this arrangement does not always provide a sufficient barrier to moisture, dust, and other debris. Another common way to wrap pallets is the use of a shrink hood, which is generally in the form of a bag placed over a pallet, which is then exposed to heat, to shrink the hood tight around the pallet. However, the shrink hood method requires equipment and energy to generate heat.
In recent years, an alternate method to wrap pallets known as a “stretch hood” system has been gaining in popularity. The stretch hood system utilizes a gusseted bag that is stretched and placed over the pallet. Stretch hood films result in a package that provides several advantages, e.g., a stretch hooded pallet provides five sided protection to the pallet that is essentially water and dust proof, especially as compared to a stretch film wrapped pallet. In addition, the stretch hood film provides more holding force to the pallet and greatly helps with load stability.
Stretch hood films provide excellent protection for the contents from environmental elements. However, like other plastic films, stretch hood films are subject to moisture condensation inside the hood. Generally, when a pallet wrapped with a plastic film is exposed to sunlight, the temperature inside the hood will rise, very much like a green-house effect. Moisture inside the packaged materials, for example in paperboard boxes, is evaporated by the heat. If the outside temperature is subsequently reduced, as typically occurs at night, the film temperature can be reduced below the dew point and moisture in the air will condense, typically as tiny droplets on the inside film surface. These tiny droplets can coalesce together into larger ones and run down the film. The amount of water is sometimes significant enough to cause damage to the contents and is a potential environment for mold growth. Produce packaging companies are especially concerned about this phenomenon. The condensation phenomena occurs quite often in the morning when the inside temperature is raised by sunlight, but the temperature outside and film temperature are still low.
Various approaches have been attempted to address the problem of condensation on the film surface. In one example, holes or perforations are mechanically punched into the film to vent moisture. Though it is widely used in certain grocery applications, perforations have only limited effectiveness for stretch hood applications because while the perforations allow moisture to leave the pallet, they also allow moisture and dust to enter, thereby eliminating any net benefit.
In another example, microporous films are used that consist of a high concentration of mineral fillers, such as calcium carbonate, that are stretched to create micropores. However, microporous films, such as films used in diapers and hygiene products, lack stretch capacity and transparency that are preferred in stretch hood applications.
Opaque bag films have also been used and are effective in blocking out sunlight and hence moisture condensation. However, opaque films are not preferred due to the lack of transparency, which prevents visual inspection of the contents and reading, for example, of a barcode on the object disposed inside the film. It is also generally known to include pigment additives to packaging films for aesthetic purposes, e.g., to prevent discoloration when the film is stretched, and to improve mechanical properties, such as tear resistance, of the film.
Alternatively, the goods are sometimes covered by a large bag that is strapped over, leaving the bottom loose. However, such a loose bag approach does not provide much protection against rain or dust and, depending on the strapping, moisture can still be trapped inside the bag in certain areas.
Accordingly, there is a need for a film that can be used in packaging applications, such as a stretch film, top sheet, loose bag, and/or stretch hood, that overcomes one or more of the above-noted deficiencies in existing packaging films.